According to a U.S. national security official with knowledge of the investigation, U.S. investigators are considering multiple suspects, including North Korea, in their investigation into a cyber attack on Sony Pictures Entertainment that knocked out the company’s computer systems for over a week. The official, who asked to remain anonymous, told Reuters on Tuesday that the forensic investigation is in its early stages, and that no clear suspects have emerged. But the official said multiple suspects are being assessed, including the North Korean government, other nations and private parties. The hack, which was launched Nov. 24, caused Sony Pictures Entertainment to shut down its internal computer network. The FBI warned U.S. businesses on Monday that hackers have used malicious software to launch a destructive cyberattack in the United States, in a private report that cybersecurity experts say described the malicious software used in the Sony attack.